The present invention relates generally to a data recording system for recording data relating to position information and specific functions in a control track of a magnetic tape, and is applicable particularly, but not exclusively, to video tape recorders (which will hereinafter be referred to as VTRs).
In conventional VTRs, a data recording/reproducing system based upon the so-called CTL coding system, in which data relating to tape-position information and comment information are recorded in a control track with the duty cycle modulation (e.g., PWM) of control pulses (CTL pulses), is employed for enabling users to access a desired position randomly. Since various types of data are selectively recorded on a control track and reproduced therefrom, such a data recording system can be lower-priced in construction as compared with the SMPTE time code recording/reproducing system which records the absolute position of a magnetic tape with respect to the recording start position with the absolute position being expressed in a pulse form and, in addition, allows freely recording various information with an extremely simple operation.
Since it is general that the period of the control pulses is one frame period (1/30 sec. period in NTSC systems), in the method of recording data with the duty cycle of the control pulses being arranged to be variable, the data transmission bit rate is extremely small to be 30 bits per second and, in the case of recording a code such as a time code which is constructed as a data block with a great number of bits, the recording/reproduction of one data block consumes several seconds. When recording the time code by means of the CTL coding system, since the CTL cording system is records only one bit per frame, it is impossible to directly record the code format in the same manner as the SMPTE time code which is constructed with 80 bits per frame. Thus, the address code is treated as the time data and recorded on a tape at a predetermined time interval (for example, every minute) so that the frame counter is reset at the address code and counts the CTL pulses for indicating a playing time. There is a problem which arises with such a CTL coding system, however, in that the timing of resetting is shifted if even one of the data in the address code is lost. In addition, in the case of an NTSC color signal, because a nominal frame number is 29.97 frames per second, the time code substantially becomes difficult to be coincident with the real time.